1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus using the same, and in particular, to a zoom lens and an image pickup apparatus which are suitable for a compact digital camera.
2. Description of the Related Art
In recent years, digital cameras in which, an arrangement has been made such that an object is photographed by using a solid image pickup element such as a CCD (Charge Coupled Device) and a CMOS (Complementary Metal Oxide Semiconductor) have become main stream, replacing a silver-salt film camera. Furthermore, such digital cameras have been used in a wide range of categories from a high-function type for professional use to a portable popular type.
A user of such digital camera of the popular type seeks to enjoy photography by capturing readily a wide variety of scenes anytime and anywhere. Therefore, a small-size product, particularly a slim digital camera, which can be accommodated easily in a pocket of clothes or a bag and carried conveniently, has been preferred. Therefore, further small-sizing of a taking lens system has been sought.
Furthermore, in order that capturing can be carried out also in a condition where a level of contrast of lightness is high, a digital camera which carries out image processing such as widening a sensitivity area of dynamic range has also been proposed, and photography in which capture conditions are not to be selected has become possible. In such camera, for photography including photography at dark places, electronic correction of the level of contrast is possible to certain extent, and furthermore, by adopting a fast lens with a large lens aperture, it is also possible to deal with photography even at darker places, and it is possible to widen conditions under which the photography is possible.
In the fast lens with a large aperture, photography with clarity is possible even with a small quantity of incident light. Accordingly, it is possible for a photographer to select a large number of capturing conditions such as increasing a shutter speed in continuous capturing of a moving object, to further higher speed. Therefore, in recent years, a fast lens with a large lens aperture has been drawing attention.
On the other hand, from a point of view of widening of a capture area, the demand for high magnification zoom is still there, and further higher magnification has been anticipated.
As a small-size zoom lens with a comparatively higher zoom ratio and fast aperture, a zoom lens which includes in order from an object side, a first lens unit having one positive lens, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power has been disclosed as a first embodiment in Japanese Patent Application Laid-open Publication No. 2009-276794.